This invention relates generally to controlling front and rear steering arrangements and more particularly to a method for synchronizing front and rear steering arrangements.
Various arrangements are known in which front and rear steering arrangements are used to control the steering of a machine. In these known arrangements, the steering has normally been independent of each other. Consequently, it was up to the skill of the operator to control the rate of steering of each of the front and rear steering arrangements. Other systems are known in which one form of steering control is used to steer one end of the vehicle and independently controlled brakes are used to slow one or the other side of the machine on the other end of the machine. Such systems are well known on agricultural machines, such as farm tractors and combines. In these known systems, the one end of the machine is steered by steerable wheels, such as an ackerman type steering and the other end of the machine is steered by slowing down one of the drive wheels relative to the other. This is normally accomplished by the operator selectively applying a brake force through the application of independently controlled brakes.
In machines commonly known as half-track machines, the front wheels are ackerman type steering with the respective wheels being steerable wheels and the rear portion of the machine has continuous tracks on each side. In these types of machines, steering of the front wheels forces the tracked portions to follow. Since it is well known that continuous tracks resists being turned, a greater steer input must be made through the ackerman steer to overcome the resistance. Normally, a portion of the steer input is lost due to the front steerable wheels sliding laterally. If the surface being traversed is soft a greater portion of the steer input is lost due to the steerable wheels sliding laterally. In order to aid in the steering of half-tracked machines, independently controlled brakes are used to slow the appropriate track with respect to the other track. The amount of independent brake effort is based on the skill of the operator.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the subject invention, a method is provided to synchronize the steering between steerable wheels on one end of a machine and non-steerable drive units on the other end of the machine. The method includes the steps of sensing the angle of the first steering arrangement, sensing the relative difference between the speeds of the drive units of the second steering arrangement, selecting a desired steer input, directing a steer input command to one of the first and second steering arrangements, calculating the angle of steer required for the other steering arrangement to match the angle of steer of the one steering arrangement, and directing a command signal to the other steering arrangement to provide a steer angle that matches the steer angle of the one steering arrangement.